AR Wiki is an easy to use app designed to allow one to browse Wikipedia while walking. It creates a Wikipedia browser window centered in your Android device, with the rear-facing camera displaying a live feed surround the Wikipedia article. In this way you can browse Wikipedia while you are walking without fear of walking into a tree or a street.
You can buy AR Wiki on the Android Market here.
Update 4/2012 This is now open source and hosted on GitHub. Check it out at my GitHub page.